Magnesium material and use of the same

ABSTRACT

An Mg material consisting of a matrix with a C long-fiber reinforcement, wherein to improve the strength of the material transversely with respect to the fiber direction the C long fibers are provided with a thin layer, wherein at least one element of the layer material of the thin layer forms a homogeneous chemical reaction layer with the respective C long fiber and wherein the thin layer forms a diffusion barrier so that the local formation of relatively coarse reaction products of alloying elements from the matrix with the C long fibers, which act as crack initiators, is prevented. Uses of the Mg material according to the invention are also described.

The invention relates to a magnesium material (hereinafter referred toas Mg material), as set forth in the classifying portion of claim 1, anduses thereof.

In order to make Mg materials with a C long-fiber reinforcement suitablefor technical uses, it is necessary for the strength thereoftransversely with respect to the fiber direction to be considerablyimproved. For that purpose, the material must involve improved bondingof the carbon fibers (C fibers) to the matrix. In addition, it isnecessary to prevent alloying elements of the matrix forming at thefibers locally relatively coarse chemical reaction products because suchreaction products act as crack initiators and reduce the level ofmechanical strength.

Therefore the object of the invention is to provide an Mg material ofthe kind set forth in the opening part of this specification, whosestrength transversely with respect to the fiber direction isconsiderably improved, wherein alloying elements of the matrix whichform relatively coarse chemical reaction products at the fibers areavoided.

In accordance with the invention that object is attained by the featuresof claim 1. Preferred configurations of the Mg material according to theinvention are characterised in claims 2 through 8.

Uses according to the invention of the Mg material according to theinvention are claimed in claims 9 through 11.

In accordance with the invention the C long fibers are provided with athin layer which performs the following functions:

-   -   at least one element of the layer material forms with the        respective C long fiber a thin, sufficiently homogeneous        chemical reaction layer;    -   the thin layer acts as a diffusion barrier in such a way that        the local formation of relatively coarse chemical reaction        products of alloying elements of the matrix at the C long fibers        is prevented; and    -   at least one element of the material of the thin layer forms an        intermetallic or intermediate compound or mixed crystal zone        with the matrix.

In the Mg material according to the invention the layer material isdesirably formed by carbide-forming agents. This can involve for exampleAl, Cr, Ti, Ta, Nb, Hf, Zr or alloys for example on an Ni basis, whichcontain carbide-forming agents.

The thin layer of the C long fibers can be produced by PVD processes(physical vapor deposition) or by CVD processes (chemical vapordeposition). The PVD process preferably involves sputtering. The CVDprocess can involve a galvanic, wet-chemical or currentlesslyelectrochemical process.

The thin layer of the C long fibers can be of a thickness in the regionof between some nm and some μm.

The Mg material according to the invention has the advantage of asufficient level of transverse strength while known C fiber-reinforcedMg materials are in practice not used because their strengthtransversely with respect to the fiber direction is too low.

In accordance with the invention the Mg material according to theinvention comprising a matrix with a C long-fiber reinforcement can beused to produce pistons of internal combustion engines. Conventionalpistons of internal combustion engines usually comprise steel or an Alalloy. A desired reduction in weight in comparison with pistons of steelor Al alloys can be achieved by the use of Mg alloys. Hitherto howeverthey have not enjoyed sufficient strength, rigidity and creepresistance. As is known a slight increase in strength can be achieved ifsuch Mg alloys are reinforced with short fibers or with suitableparticles. That slight increase in strength however is still notsufficient. Adequate strength, rigidity and creep resistance is onlyachieved with the Mg material according to the invention comprising amatrix with a C long-fiber reinforcement, wherein the C long fibers areprovided with a thin layer of the above-indicated kind. In the case ofthe Mg material according to the invention the interface strength asbetween the C long fibers and the matrix is optimised. By virtue of asuitable configuration and fiber arrangement, when using the Mg materialaccording to the invention in pistons of internal combustion engines, itis possible to achieve a saving in weight of up to 30%. The compositematerial according to the invention consisting of the matrix and the Clong-fiber reinforcement has levels of strength which are comparable tothose of high-strength Al alloys, in the critical regions and directionsof an internal combustion engine piston. The rigidity levels are evenhigher than the high-strength Al alloys. Force-application regions suchas for example the bearing bosses for gudgeon pins, grooves for pistonrings and possibly piston crowns or combustion chambers can be in theform of inserts which in turn can be made from higher-strength metalalloys or from composite materials and which, with the componentconsisting of the Mg material according to the invention, form acomposite assembly joined in positively locking relationship and/orjoined by the materials involved.

The Mg material according to the invention comprising a matrix with a Clong-fiber reinforcement, wherein the C long fibers are provided with athin layer, as has been described hereinbefore, can also be used inaccordance with the invention for the production of connecting rods ofinternal combustion engines. The connecting rods used in internalcombustion engines at the present time usually comprise steel or a Tialloy. Tests have also already been conducted with GRP and CRPconnecting rods. A reduction in weight in comparison with connectingrods of steel or Ti alloys can be achieved by the use of Mg alloys.However they do not offer adequate strength and rigidity. A slightincrease in strength is possible if such Mg alloys are reinforced withshort fibers or with particles. However such an increase in strength isstill not sufficient. Adequate strength and rigidity are first affordedby the use of the Mg material according to the invention comprising amatrix with a C long-fiber reinforcement with a thin layer, as has beendescribed hereinbefore, by which the interface strength between thematrix and the C long fibers is optimised. By virtue of a suitableconfiguration and fiber arrangement, it is possible to achieve a savingin weight of up to 70% with the Mg material according to the invention,in respect of connecting rods. In the critical regions and directions ofconnecting rods, the Mg material according to the invention affordslevels of strength which are comparable to those of high-strength Alalloys. The levels of rigidity are even higher than those of Ti alloys.Force-application regions such as the bearing eyes for the gudgeon pinsand for the crank pins can be in the form of inserts which in turn canbe made from higher-strength metal alloys or from composite materials.Those inserts can form with the component of the Mg material accordingto the invention a composite assembly joined in positively lockingrelationship and/or by the materials involved.

In accordance with the invention the Mg material according to theinvention can also be used for the production of propulsion bases forsub-caliber projectiles and shells. Known propulsion bases usuallycomprise high-strength Al alloys. A reduction in weight can be achievedwith such propulsion bases by the use of Mg alloys. The known Mg alloyshowever are not of sufficient mechanical strength. Only slight increasesin strength are possible with known Mg alloys, by means of short-fiberor particle reinforcements. It is here that the Mg material according tothe invention provides a remedy so that, by virtue of a suitableconfiguration and fiber arrangement of the Mg material according to theinvention, it is possible to achieve a saving in weight of between about20 and 30%. The Mg composite material according to the invention with Clong-fiber reinforcement with the thin coating, as has been describedhereinbefore, is of levels of strength which are comparable to those ofhigh-strength Al alloys, in critical regions and directions. The levelsof rigidity are even higher than the high-strength Al alloys.Force-application regions such as for example a screwthread in relationto the penetrator can be in the form of inserts which in turn can beproduced from higher-strength metal alloys or from composite materialsand which can be connected to the component, that is to say thepropulsion base, comprising the Mg material according to the invention,in positively locking relationship and/or by way of the materialsinvolved.

1. An Mg material comprising a matrix with a C long-fiber reinforcementcharacterised in that the C long fibers are provided with a thin layer,wherein at least one element of the layer material forms a homogeneouschemical reaction layer with the respective C long fiber, and the thinlayer forms a diffusion barrier so that the local formation ofrelatively coarse reaction products of alloying elements from the matrixwith the C long fibers is prevented.
 2. An Mg material as set forth inclaim 1 characterised in that the layer material of the thin layer isformed by carbide-forming agents.
 3. An Mg material as set forth inclaim 2 characterised in that the layer material of the thin layer isformed by Al, Cr, Ti, Ta, Nb, Hf and Zr.
 4. An Mg material as set forthin claim 2 characterised in that the layer material of the thin layer isformed by alloys on an Ni basis, which contain carbide-forming agents.5. An Mg material as set forth in one of claims 1 through 4characterised in that the thin layer is produced by a PVD or CVDprocess.
 6. An Mg material as set forth in claim 5 characterised in thatthe thin layer is applied to the C long fibers by sputtering.
 7. An Mgmaterial as set forth in claim 5 characterised in that the thin layer isapplied to the C long fibers galvanically, wet-chemically or by acurrentlessly electrochemical process.
 8. An Mg material as set forth inone of claims 1 through 7 characterised in that the thin layer is of athickness in the range of between some nm and some μm.
 9. Use of an Mgmaterial as set forth in one of claims 1 through 8 for the production ofpistons of internal combustion engines.
 10. Use of an Mg material as setforth in one of claims 1 through 8 for the production of connecting rodsof internal combustion engines.
 11. Use of an Mg material as set forthin one of claims 1 through 8 for the production of propulsion bases forsub-caliber projectiles.